纳米块结构的氧化铁薄膜制备、表面修饰及光解水性能研究

Hydrogen is regarded as clean and renewable fuel in the future because of its high-energy capacity and environmental friendliness. Solar energy stored in Hydrogen is a considerable attraction to solving the energy challenge. Hematite (a-Fe2O3) has been extensively investigated as one of the best candidates for photoanode semiconductor due to its excellent chemical stability in aqueous solution, abundance in the earth, and low cost. In this project, ultrathin nanocube structure of a-Fe2O3 film on FTO substrate will be synthesized for the consideration of extremely short hole diffusion length. The ultrathin film is beneficial to facilitating charge transfer and minimizing bulk charge recombination due to the short distance of photogenerated electrons transferring to FTO substrate and hole transporting to a-Fe2O3/electrotye surface. Meantime, phosphate ions and Co-Pi can be coated on the hematite films. The former will establish a negative electrostatic field on hematite surface, which promotes charge separation and extraction of photoexcited holes to the electrode surface. The latter can improve inert oxygen evolution reaction (OER) kinetics which results in increased water oxidation efficiency. Phosphate ions adsorption on hematite through bidentate binding provide a high stability of the photoanode. A PV-PEC based device will be fabricated for efficient solar conversion since PV cell provides voltage needed for water splitting. The project is aiming to provide high efficient and stable a-Fe2O3 photoanode through nanocube structure and surface modification. The effect of phosphate ions on the morphology, and effects of surface characteristics and modification on the photoelectrochemical properties of the hematite thin films were investigated. The mechanism for the formation of nanocube structure of a-Fe2O3 was proposed. The results present a facile method which combined the morphology control and surface modification together for a better photoelectrochemical performance of hematite thin films.

太阳能光催化分解水制氢研究对开发利用太阳能、实现节能减排具有重要意义。项目选用价格低廉、与环境友好的a-Fe2O3为催化材料制备光阳极，应用于光电催化分解水制氢反应。针对a-Fe2O3光生空穴传输距离短的问题，通过形貌调控，由水热法制备超薄纳米块a-Fe2O3，缩短光生电子向FTO基体以及空穴向界面传输的距离，减少体相内电荷复合。同时，用磷酸根或磷酸钴对薄膜表面进行修饰，因为磷酸根基团可形成负静电场，促进空穴向界面迁移；磷酸钴有提高产氧速率、促进空穴注入到电解液的作用。利用课题组制备的染敏电池(DSC)，开发光伏-光催化耦合分解水制氢体系，提高太阳能-氢能转换效率。项目通过形貌控制和表面修饰以制备高效、稳定的a-Fe2O3光阳极为主线，深入研究形貌、表面修饰物对电荷分离、传输以及光电催化性能的影响，阐明纳米块的形成机理，为制备新型形貌的薄膜电极和光伏-光电耦合催化体系提供新思路和实验方法。

通过光电手段分解水获取氢气，将太阳能转换成氢能，对实现能源的可持续发展具有重要的现实意义。纳米ɑ-Fe2O3材料因具有储量丰富、性质稳定、无毒和光催化活性高的特点而成为了目前新型光解水材料的研究热点之一。ɑ-Fe2O3是n型间接带隙半导体，其禁带宽度Eg约为2.1eV，较窄的禁带宽度能够使其光吸收波长达590 nm。但是，纳米ɑ-Fe2O3存在导电性差，空穴传输距离短，电子-空穴复合几率高，表面空穴氧化水的反应速率慢等缺点，严重限制了其光解水的效率。项目开展了元素掺杂、表面催化剂修饰以及形貌调控等手段，提高材料的导电性能以及表面催化活性，减少载流子在体相和界面的复合，进而提高材料整体光电催化性能。采用Sn、Ti、Mn、Co、Ag等金属元素对半导体进行掺杂，并采用磷酸盐对α-Fe2O3表面修饰以及形貌调控。研究发现，Ag和Co有机金属配合物修饰α-Fe2O3表面，起到表面催化作用，甲基咪唑的配合作用有效抑制了外界电压对Co的氧化作用，而Co-MOF中的单原子分散的Co通过Co2+/Co3+可逆转化，吸附水中OH和OOH的反应活性物质，促进水氧化反应；MoO42-通过钝化α-Fe2O3表面态缺陷，减少光生电子空穴表面复合几率，进而提高了注入效率和光电流；Ti和Sn元素掺杂ɑ-Fe2O3，提高材料的导电性能以及表面催化活性，减少载流子在体相和界面的复合，进而提高了光生电荷分离效率。采用价廉的磷酸盐控制-Fe2O3纳米颗粒的生长，获得纳米块结构的薄膜，光生电子与空穴向界面传输距离短，减少体相中电荷复合；同时，在薄膜表面负载磷酸根离子，形成的负静电场，进一步促进了空穴迁移，提高电荷注入效率。采用简单、快速的旋涂法制备SnS薄膜，以水合肼为还原剂经加热还原生成致密的、纯相位的SnS薄膜，作为吸光电材料应用在太阳能电池研究中。此外，开展了钙钛矿太阳能电池的研究, 设计合成一些结构新颖的空穴传输材料，应用于钙钛矿电池的空穴传输层，获得一些有价值的研究结果。基于M109的钙钛矿太阳能电池获得了18%的光电转化效率，以及高达1.11伏的开路电压，为构成钙钛矿太阳能电池串联与价廉高效光阳电极组成光伏-光电解水制氢装置，提供实验数据和研究基础。